This invention relates to a process for extracting bismuth from a bismuth-bearing material, in which the material is smelted in a furnace with the addition of at least one flux capable of slagging the gangue. A phase containing the bismuth is formed and separated from the slag.
As used herein, the term "bismuth-bearing material" means ores and concentrates of bismuth in the roasted or unroasted state, mixed ores and concentrates of bismuth and another metal such as copper, in the roasted or unroasted state, and bismuth-bearing metallurgical by-products such as sulphated or oxidized flue dust. These bismuth-bearing materials normally contain at least 2% by weight of bismuth.
It is known to treat oxidized bismuth concentrates by reduction smelting, mixed sulphurized-oxidized bismuth concentrates by roasting and reduction smelting, and sulphurized bismuth concentrates either by roasting and reduction smelting or by cementation smelting.
Cementation smelting is carried out in a crucible furnace in which the bismuth-bearing material is smelted, and to which is added a flux and a metal, such as iron, which has a stronger affinity for sulfur than bismuth. Three phases are formed: a lower layer constituting the metallic phase and comprising the bismuth in metallic form; an intermediate layer comprising matte containing the sulphide of said other metal; and an upper layer of slag comprising the elements of the gangue.
Reduction smelting is carried out in a reverberatory furnace or in a crucible furnace and yields a metallic phase comprising the bismuth in metallic form and a slag phase comprising the elements of the gangue.
Since bismuth is a very volatile metal, these known processes require the use of soda ash or fluor-spar as a flux in order to obtain slags with a low melting point (of about 1000.degree. C.).
The foregoing conventional processes therefore suffer the drawbacks of requiring expensive fluxes for the smelting and yielding very corrosive sodic slags during the smelting.
Accordingly, it is an object of the present invention to provide an improved process for extracting bismuth from bismuth-bearing materials.
Another object is to provide a process for the pyrometallurgical extraction of bismuth from bismuth-bearing materials without the use of expensive fluxes and the formation of caustic sodic slags.
These and other objects of the invention and the advantages thereof can be had by reference to the following description and claims.